1. Field of the Invention
The present invention relates to a method of plugging the end of a leaking heat exchanger tube and a plug for doing so.
2. Description of the Prior Art
Heat exchanger tubes may develop leaks for many reasons, such as pitting, corrosion, fatigue cracks, steam erosion and other types of damage. Tube leaks reduce heat exchanger efficiency, and when enough tubes develop leaks to seriously effect the operation of the heat exchanger, but not enough to require a replacement of the leaking tubes, the practice is to shut the heat exchanger down long enough to plug the ends of the leaking tubes.
Leaking tubes have been plugged in the past by fusion welding a plug in, or a cap on, the ends of the tube at the tube sheet. This method is extremely cumbersome and time consuming.
Tapered plugs have also been used to seal off heat exchanger tubes. The plugs are inserted into the end of the tube at the tube sheet such that the plug is pressed tightly within the tube. The larger end of the tapered plug remains partially outside of the tube to provide a means for later removing the plug. Such plugs, however, may easily be inserted too far into the tube or with too much force, resulting in damage or "dimpling" of the tube sheet, which creates a major problem.
Explosively expanded plugs for plugging heat exchanger tubes at the juncture of the tube and tube sheet are known in the art. Some are moved into engagement with the tube at a velocity sufficient to weld the plug to the tube. However, the welded plugs cannot be easily removed from the tube ends when it becomes necessary to remove and replace the damaged tubes. See U.S. Pat. Nos. 3,555,656, 3,590,877, 3,785,291, 3,724,062, and 3,919,940.
Other prior art plugs are explosively expanded sufficiently to form a metal-to-metal seal. There is a problem with this type of plug. As the temperature in the heat exchanger varies, the tubes expand and contract, which can cause sufficient relative movement between the plugs and the tubes to break the metal-to-metal seal. See U.S. Pat. No. 3,491,798 for a description of this type plug.
Therefore, it is an object of this invention to provide a metal-to-metal seal type of explosively expanded plug with one or more resilient seal rings that will maintain a pressure-tight seal between the plug and the tube should the metal-to-metal seal be broken due to expansion and contraction of the tube and a method on installing the plug.
It is another object of this invention to provide a plug for sealing the opening in a tube sheet or the open end of a tube located in an opening in a tube sheet with a generally cylindrical metallic body of ductile material for positioning in the open end of the tube with a resilient seal ring and an explosive charge in a longitudinal opening in the body, that when detonated expands the body and the seal ring into sealing engagement with the tube sheet or with the tube to plug the end of the tube.
These and other objects, advantages, and features of this invention will be apparent to those skilled in the art from a reading this specification including the attached drawings and appended claims.